1. Field of the Invention
The invention relates to a lamp and an illumination system and a driving method thereof, and more particularly, to a light emitting diode (LED) lamp and an illumination system and a driving method thereof.
2. Description of Related Art
In the past 20 years, people have been working hard on the development of new illumination sources. It is specified in the “Rainbow Project” funded by the European Union (EU) that a new illumination source should satisfy such four conditions as high efficiency, low power consumption, zero pollution, and close resemblance to natural light. Because a light emitting diode (LED) possesses aforementioned characteristics and is far superior to conventional illumination sources (for example, incandescent lamp and fluorescent lamp), the LED is widely considered a green light source in the 21st century and adopted for replacing incandescent lamp and fluorescent lamp as a leading product in the illumination source market.
Generally speaking, an LED lamp with a dimming function directly emits light according to a pulse width modulation (PWM) signal generated by a dimmer. To be specific, a driver in the LED lamp directly drives the LEDs according to the PWM signal generated by the dimmer. Besides, a frequency of the driving signal generated by the driver in the LED lamp according to the PWM signal generated by the dimmer for driving the LEDs is equal to a frequency of the PWM signal generated by the dimmer.
However, because the PWM signals generated by dimmers from different manufacturers have different but fixed frequencies (usually fall within a range of 100 Hz-1 KHz), if the selected dimmer generates a PWM signal of a low but fixed frequency (for example, 100 Hz), flickering of the light source provided by the LED lamp is easily detected by the human eye (this is because the frequency of the PWM signal generated by the dimmer is very close to the frequency range detectable to the human eye).
On the other hand, if the selected dimmer generates a PWM signal of a high but fixed frequency (for example, 1 KHz), signal interference between different components of the driver in the LED lamp is greatly increased, and the complexity in designing an electromagnetic-interference-free (EMI-free) circuit is greatly increased (this is because the frequency of the PWM signal generated by the dimmer not only interferes with the signal transmission between different components of the driver in the LED lamp but also increases the overall EMI index of the LED lamp).
Additionally, the Taiwan Patent No. M381241, M371263, and 1297819, the Taiwan Patent Publication No. 201019008, and the U.S. Pat. Nos. 7,560,677 and 7038399 disclose techniques for driving an LED lamp.